Measuring cylindrically symmetric refractive-index profiles: a method

This paper describes a new nondestructive method to measure cylindrically symmetric refractive-index profiles of transparent cylinders. The technique is based on the measurement of the axial displacement of rays that are refracted within the cylinder. Three different types of index profile were experimentally determined. Profile errors of better than one part in 10(3) were achieved using very modest equipment. The effects of certain experimental parameters on the profile accuracy are noted. The technique may be applied to the characterization of optical fiber preforms and graded-index rod lenses.     

Stepwise graded refractive-index profiles for design of a narrow-bandpass filter

A combination of stepwise graded refractive-index profiles and a cavity structure is used for designing narrow-bandpass filters of TiO(2)/SiO(2) multilayer films upon BK7 glass substrates. Symmetrical profiles of stepwise graded refractive indices result in high transmittance of passbands for the designed filters. The bandwidth of the narrow-bandpass filter is controlled by adjustment of parameters such as the thickness and the number of layers in the multilayer stack. This design is proposed as a new and simple method for coating synthesis of optical filters.     

Reconstruction of fiber grating refractive-index profiles from complex bragg reflection spectra

Reconstruction of the refractive-index profiles of fiber gratings from their complex Bragg reflection spectra is experimentally demonstrated. The amplitude and phase of the complex reflection spectrum were measured with a balanced Michelson interferometer. By integrating the coupled-mode equations, we built the relationship between the complex coupling coefficient and the complex reflection spectrum as an iterative algorithm for reconstructing the index profile. This method is expected to be useful for reconstructing the index profiles of fiber gratings with any apodization, chirp, or dc structures. An apodized chirped grating and a uniform grating with a depression of index modulation were used to demonstrate the technique.     

Direct deflection method for determining refractive-index profiles of polymer optical fiber preforms

We present a method for determining the refractive-index profile of polymer optical fiber preforms through a direct-deflection measurement. The method is simple to use, compact, and has good resolution. The profile is obtained from the deflection data by numerically integrating the differential-ray equation for a radial refractive-index gradient. Corrections for topographical deviations are also discussed. Results for both graded-index and step-index fibers are presented.     

Concurrent three-dimensional characterization of the refractive-index and residual-stress distributions in optical fibers

A three-dimensional index-stress distribution (3DISD) measurement method for determining concurrently the refractive-index distributions (RIDs) and residual-stress distributions (RSDs) in optical fibers is presented. The method combines the quantitative-phase microscopy technique, the Brace-K?hler compensator technique, and computed tomography principles. These techniques are implemented on a common apparatus to enable concurrent characterization of the RID and the RSD. Measurements are performed on Corning SMF-28 fiber in an unperturbed section and in a section exposed to CO₂ laser radiation. The concurrent measurements allow for the first accurate comparison of the collocated RID and RSD. The resolutions of the refractive index and stress are estimated to be 2.34×10^-5 and 0.35?MPa, respectively.     

Construction of refractive-index profiles of planar waveguides with additional information obtained from surface plasmon resonance

A surface plasmon resonance (SPR) is excited between a metal film and a graded-index planar waveguide. After the propagation constant of the SPR is measured, the refractive index near the surface of the waveguides, which is difficult to obtain by conventional techniques, is determined experimentally. With this nondestructive technique, combined with the inverse analytical transfer matrix method, the planar waveguide can be profiled to a high degree of accuracy.     

Spectroscopic ellipsometry of slightly inhomogeneous nonabsorbing thin films with arbitrary refractive-index profiles: theoretical study

We develop a new approximation for the amplitude reflection coefficients of a slightly inhomogeneous thin film. This approximation incorporates exactly the interference effects at the substrate and the ambient interfaces. Interference effects inside the inhomogeneous film are incorporated in the Born approximation. We also develop a new approach to the reconstruction of the refractive-index profile from ellipsometric spectra. It is based on a physically sound parameterization of the refractive-index profile. The new approach is tested on the model reconstruction problem.     

Controlled surface modification of boron nitride nanotubes

Controlled surface modification of boron nitride nanotubes has been achieved by gentle plasma treatment. Firstly, it was shown that an amorphous surface layer found on the outside of the nanotubes can be removed without damaging the nanotube structure. Secondly, it was shown that an oxygen plasma creates nitrogen vacancies that then allow oxygen atoms to be successfully substituted onto the surface of BNNTs. The percentage of oxygen atoms can be controlled by changing the input plasma energy and by the Ar plasma pre-treatment time. Finally, it has been demonstrated that nitrogen functional groups can be introduced onto the surface of BNNTs using an N(2) + H(2) plasma. The N(2) + H(2) plasma also created nitrogen vacancies, some of which led to surface functionalization while some underwent oxygen healing.     

钠基蒙脱土的有机改性及其表征

为了改善蒙脱土的层间结构,采用十六烷基三甲基溴化铵(CTAB)与十八烷基三甲基氯化铵(OTAC)对钠基蒙脱土进行有机插层改性,并且考察了有机阳离子种类、反应温度、pH值及有机阳离子加入量对插层效果的影响。使用X射线衍射仪 (XRD)、傅里叶变换红外光谱仪(FTIR)、热重分析(TGA)、扫描电镜(SEM)与透射电镜(TEM)对样品进行了系统的分析。结果表明,OTAC插层效果比CTAB好,适宜的改性温度为80℃,在一定的范围内,pH的减小有利于插层,有机阳离子加入量为2倍于阳离子交换容量(CEC)时插层效果最理想。在此条件下,成功制备了有序高层间距纳米有机蒙脱土,晶面间距达到4.12 nm,甚至有部分片层剥离。     

二氧化硅凝胶的疏水改性及表征

以正硅酸乙酯为原料,经溶胶-凝胶过程制备二氧化硅溶胶,再利用二甲基二乙氧基硅烷(DDS)对其进行改性,制备疏水性二氧化硅凝胶.用红外光谱、接触角,热重分析及原子力显微镜等测试方法对试样的结构、疏水性、热稳定性及形貌进行分析.结果表明,改性后的样品是表面存在疏水基团—CH3的疏水凝胶;热稳定性较好,600℃之后没有明显的质量损失,热处理温度定于400℃可保证其疏水性;表面均一平整,孔隙率较高.     

Microinterferometric optical phase tomography for measuring small, asymmetric refractive-index differences in the profiles of optical fibers and fiber devices

A new technique, microinterferometric optical phase tomography, is introduced for use in measuring small, asymmetric refractive-index differences in the profiles of optical fibers and fiber devices. The method combines microscopy-based fringe-field interferometry with parallel projection-based computed tomography to characterize fiber index profiles. The theory relating interference measurements to the projection set required for tomographic reconstruction is given, and discrete numerical simulations are presented for three test index profiles that establish the technique's ability to characterize fiber with small, asymmetric index differences. An experimental measurement configuration and specific interferometry and tomography practices employed in the technique are discussed.     

纳米粒子的表面聚合物接枝改性

综述了纳米粒子与高分子聚合物复合的优点及不足,分析引起不足的原因,指出纳米粒子表面改性的重要性。同时在比较纳米粒子几种表面改性方法的基础上指出化学接枝改性的优越性,分析各种化学接枝改性方法及其有关的修饰机理和几种常用的表征方法。     

Controlled synthesis and structural characterization of polycrystalline GaSe

A comprehensive study on the synthesis and characterization of gallium selenide (GaSe) has been reported in this paper. Synthesis of gallium selenide (GaSe) from component elements has been carried out in a specially designed and fabricated quartz ampoule, with the help of a rocking furnace. X-ray diffractometry study revealed crystalline GaSe samples belonging to hexagonal system. Raman spectral study emphasized three sharp lines at 208.89, 253.95, and 306.52 cm⁻¹, in good agreement with X-ray diffraction results. Scanning electron microscopy revealed particles of rock like structure, sized in the range 0.4–6 μm.     

Controlled growth and characterization methods of semiconductor nanomaterials

One-dimensional (1D) semiconductor nanomaterials attract much attention because they are ideal systems for investigation and studying the relationship between properties and structures and having extensive application future in the high technical field. They are expected to play an important role in fabrication of the next generation nanocircuits, nanotools, nanowires lasers, photon tunneling devices, near-field photo-waveguide devices, etc. This article described controlled growth, characterization of structures and morphologies and properties of 1D semiconductor nanomaterials based on our previous works. This article is organized into two parts: The first part is complicated nanostructures of semiconductors, which includes coaxial nanocables, heterostructure nanowires and nanowires with metal-semiconductor junction behavior, hierarchical structures, doping of the nanowires and nanobelts, porous materials and periodically twined nanowires and asymmetrical polytypic nanobelts. The second part contains semiconductor nanoarrays based on anodic alumina membrane (AAM) templates. Finally, we propose that further investigation of the influence of nanomaterial morphologies on properties and how to design the morphology of nanostructures to meet the property requirements of nanodevices are our future research directions in this field.     

Controlled synthesis and characterization of ZnSe quantum dots

Adopting improved metal-organic "Green method," Colloidal ZnSe quantum dots were synthesized by using cheap and low toxic zinc oxide (ZnO) in an organic solvent system of 1-hexadecylamine (HDA), lauric acid (LA) and tri-n-octylphosphine (TOP). The effects of HDA dosage, injection temperature, growth temperature and time on the microstructure and optical properties of ZnSe were studied by means of X-Ray diffraction(XRD), transmission electron microscopy (TEM), spectrofluorometers and ultraviolet spectrophotometer, respectively. The results showed that ZnSe quantum dots with the best range of the size evolution were obtained under the condition of injection at 280 degrees C and growth at 240 degrees C by choosing the optimal parameters of ZnO:HDA:LA= 1:2.1:5.2 and TOPSe = 1 mol/L. Its size became larger and the emission peak shifted obviously to red with increasing the growth time. Meanwhile, the obtained ZnSe was of the wurtzite structure, had good uniformity and fluorescent characteristics.     

Classification scheme and nomenclature for refractive-index distributions

A classification scheme and nomenclature for inhomogeneous refractive-index distributions is proposed which is consistent, unambiguous, and appeals to intuition. The classification is based on (1) the generic shape of the isoindicial surfaces, (2) the detailed dependence of the index on some position coordinate characterizing the isoindicial surfaces, and (3) whether the index distribution is given by N or N2 as some function of position. The scheme is illustrated by distributions which are of technological or physiological interest.